The proposed studies examine the modulation of the response to parathyroid hormone in bone by a variety of hormonal and pharmacologic agents. The cyclic AMP generated in rat bone in vivo represents the initial response to parathyroid hormone in this tissue. We have devised methods to measure cAMP in adult rat bone. Animals are treated by endocrine ablation, or hormone or drug supplementation. After appropriate periods of time, parathyroid hormone is infused by vein, the calvaria are removed and extracted and cAMP measured by a radioligand assay. BIBLIOGRAPHIC REFERENCES: Marcus, R. and F. Orner. Cyclic AMP formation in bone: interaction of prostaglandins with parathyroid hormone. Endocrinology, in press. Marcus, R. and F. Orner. Effects of thiazide diuretics on cyclic AMP production in bone. Abstract, The 6th Parathyroid Conference, Vancouver, B.C. June 1977.